Multiplexing Image Light Guide with Split Input and Optical Power

The present application is the U.S. National Stage Application pursuant to 35 U.S.C. § 371 of International Patent Application No. PCT/US23/68721, filed on Jun. 20, 2023, which application claims the benefit under Articles 4 and 8 of the Stockholm Act of the Paris Convention for the protection of Industrial Property of U.S. Patent Application No. 63/367,337, filed on Jun. 30, 2022, which applications are incorporated by reference in their entireties.

The present disclosure generally relates to electronic displays, and more particularly, to displays utilizing image light guides with diffractive optics to convey image-bearing light to a viewer.

Head-Mounted Displays (HMDs) are being developed for a range of diverse uses, including military, commercial, industrial, fire-fighting, and entertainment applications. For many of these applications, there is particular value in forming a virtual color image that can be visually superimposed over the real-world image that lies in the field of view of the HMD user. Optically transparent flat parallel plate waveguides, also called planar waveguides, convey image-bearing light generated by a color projector system to the HMD user. The planar waveguides convey the image-bearing light in a narrow space to direct the virtual image to the HMD user's pupil and enable the superposition of the virtual image over the real-world image that lies in the field of view of the HMD user.

In such conventional imaging light guides, collimated, relatively angularly encoded light beams from a polychromatic or monochromatic image projector source are coupled into an optically transparent planar waveguide by an input coupling optic, such as an in-coupling diffractive optic, which can be mounted or formed on a surface of the parallel plate planar waveguide or disposed within the waveguide. Such diffractive optics can be formed as diffraction gratings, holographic optical elements, or in other known ways. For example, the diffraction grating can be formed as a surface relief grating. After propagating along the planar waveguide, the diffracted color image-bearing light can be directed back out of the planar waveguide by a similar output grating, which may be arranged to provide pupil expansion along one or more dimensions of the virtual image. In addition, one or more diffractive turning gratings may be positioned along the waveguide optically between the input and output gratings to provide pupil expansion in one or more dimensions of the virtual image. The image-bearing light output from the parallel plate planar waveguide provides an expanded eyebox for the viewer.

A HMID system may consist of at least one image conveying waveguide for conveying virtual image-encoded light to the left eye of the viewer and at least one image conveying waveguide for conveying virtual image-encoded light to the right eye of the viewer, thus enabling stereo images to the viewer.

Current systems for virtual image reconstruction require multiple waveguides, for example, a waveguide stack, where one waveguide is utilized for each wavelength range of light. For example, a first waveguide of the waveguide stack may be used to convey light in the red wavelength range, and a second waveguide of the waveguide stack may be used to convey light in the blue wavelength range. The use of multiple waveguides increases costs as well as the potential for manufacturing defects and ingress of pollutants (e.g., dust particles, moisture, etc.). Additionally, while it is possible to overlap sets of out-coupling diffractive optic gratings to outcouple light of different wavelength ranges within the same waveguide using linear gratings, such arrangement while adding optical power adds additional complexity.

The present disclosure is directed to one or more exemplary embodiments of an image light guide.

The image light guide can include a substrate operable to propagate image-bearing light beams of a first wavelength range and a second wavelength range, an in-coupling diffractive optic comprising a first input region and a second input region, the first input region operable to couple image-bearing light of the first wavelength range into the image light guide and the second input region operable to couple image-bearing light of the second wavelength range into the image light guide, and an out-coupling diffractive optic comprising a first set of diffractive features and a second set of diffractive features, wherein the first set of diffractive features and the second set of diffractive features at least partially overlap within the out-coupling diffractive optic, wherein the first and second set of diffractive features introduce an optical power to change a focusing distance of the first wavelength range and the second wavelength range of image-bearing light beams.

In an exemplary embodiment, the first set of diffractive features and the second set of diffractive features each introduce a different optical power. In an exemplary embodiment the image light guide further comprises a first turning optic operable to turn image-bearing light received from the first input region of the in-coupling diffractive optic toward the out-coupling diffractive optic. In an exemplary embodiment, the image light guide comprises a second turning optic operable to turn image-bearing light received from the second input region of the in-coupling diffractive optic toward the out-coupling diffractive optic. In an exemplary embodiment, each diffractive feature of the first set of diffractive features is curved. In an exemplary embodiment, each diffractive feature of the second set of diffractive features is curved. In an exemplary embodiment, the out-coupling diffractive optic includes a two-dimensional array of zones, wherein each zone comprises one or more of the first set of diffractive features and the second set of diffractive features, wherein each diffractive feature of the first set of diffractive features and the second set of diffractive features is linear, wherein each zone has a common pitch between each diffractive feature of the first and second sets of diffractive features, wherein the common pitch varies between successive zones in at least a first dimension of the two-dimensional array.

In an exemplary embodiment, the first set of diffractive features vary in pitch. In an exemplary embodiment, the second set of diffractive features vary in pitch. In an exemplary embodiment, the first set of diffractive features in the successive zones along the first dimension are oriented in a constant direction, and successive zones along a second dimension of the array are oriented in different directions in a manner that progressively varies in a stepwise manner between the successive zones along the second dimension. In an exemplary embodiment, the second set of diffractive features in the successive zones along the first dimension are oriented in different directions in a manner that progressively varies in a stepwise manner between the successive zones along the first dimension, and successive zones along the second dimension are oriented in a constant direction. In an exemplary embodiment, the first wavelength range of image-bearing light comprises red light. In an exemplary embodiment, the second wavelength range of image-bearing light comprises blue light. In an exemplary embodiment, the first set of diffractive features comprises a first pitch progression and the second set of diffractive features comprises a second pitch progression, the second pitch progression being equal to the first pitch progression. In an exemplary embodiment, the first input region comprises a first pitch and the second input region comprises a second pitch. In an exemplary embodiment, at least one of the first set of diffractive features and the second set of diffractive features comprise blazed, slanted, or hybrid grating features.

The image light guide can include a frame, an image source connected to the frame, wherein the image source is operable to emit image-bearing light of a first wavelength range and a second wavelength range, and a waveguide connected to the frame, including an in-coupling diffractive optic comprising a first input region and a second input region, the first input region operable to couple image-bearing light of the first wavelength range into the waveguide and the second input region operable to couple image-bearing light of the second wavelength range into the waveguide, and an out-coupling diffractive optic comprising a first set of diffractive features and a second set of diffractive features, wherein the first set of diffractive features and the second set of diffractive features at least partially overlap within the out-coupling diffractive optic and wherein the first set of diffractive features and the second set of diffractive features are operable to form a virtual image that is viewable from a viewer eyebox, wherein at least the first set of diffractive features introduce an optical power that changes a focusing distance of the virtual image.

In an exemplary embodiment, the first set of diffractive features and the second set of diffractive features introduce an optical power and change the focusing distance of the virtual image. In an exemplary embodiment, the image light guide comprises a first turning optic operable to turn image-bearing light received from the first input region of the in-coupling diffractive optic. In an exemplary embodiment, the image light guide comprises a second turning optic operable to turn image-bearing light received from the second input region of the in-coupling diffractive optic. In an exemplary embodiment, at least one of the first set of diffractive features and the second set of diffractive features vary in pitch.

The present disclosure utilizes a split in-coupling diffractive optic that is optimized to in-couple light from two ranges of wavelengths (e.g., blue and red). The out-coupling optic includes two sets of diffractive features (e.g., one set of gratings optimized to out-couple a blue wavelength range of light and the other set of gratings optimized to out-couple a red wavelength range of light), where the two sets of output gratings overlap and are curved or segmented to introduce optical power, thereby forming a complex out-coupling optic within a single waveguide. In an exemplary embodiment, each set of out-coupling diffractive features introduces a different optical or dioptric power (e.g., the image light guide is operable to form a first virtual image at a first distance and a second virtual image at a second distance).

In an exemplary embodiment, the present disclosure provides a multi-input, multiplexed image light guide with a complex, powered, outcoupling grating, all within a single waveguide. The waveguide includes a single input split into two sections, a first section optimized for in-coupling light from within a first wavelength range (e.g., blue) into the waveguide and a second section for coupling light from within a second wavelength range (e.g., red) into the waveguide. The waveguide can also include two turning diffractive optics, one being optimized for each wavelength range. The out-coupling optic includes a complex grating pattern of two overlapping sets of gratings. The first output grating set is optimized for the first wavelength range and is chirped (i.e., has a progressively increasing pitch in one direction). The second output grating set is optimized for the second wavelength range and is also chirped in a second direction with the same progression as the first output grating set. Each grating row/column of grating features within each output grating set can be curved or segmented to introduce optical power for each respective wavelength range.

It should be appreciated that it is not necessary to optimize for green light as the wavelength range for green light is between the wavelength ranges of red and blue. Gratings that are optimized for red or blue light will still diffract light within the green range, albeit less efficiently. Thus, in an exemplary embodiment, the image light guide optimizes for red light and blue light, and image-bearing light in the green range will be in-coupled and out-coupled evenly by the red and blue gratings. It should further be appreciated that the image light guide of the present disclosure is operable to optimize two spectral ranges or wavelengths (i.e., for any pitch/wavelength range), and is not limited to optimization of just red and blue light.

In an exemplary embodiment, the path for each wavelength range includes in-coupling, even coupling within the in-coupling diffractive optic to the turning or intermediate optic, odd coupling from the turning optic to the outcoupling diffractive optic. It should be appreciated that, although not required, the image light guide described herein could be utilized to introduce 2D eyebox expansion.

These and other aspects, objects, features, and advantages of the present disclosure will be more clearly understood and appreciated from the following detailed description of the embodiments and appended claims, and by reference to the accompanying drawing figures.

It is to be understood that the invention may assume various alternative orientations and step sequences, except where expressly specified to the contrary. It is also to be understood that the specific assemblies and systems illustrated in the attached drawings and described in the following specification are simply exemplary embodiments of the inventive concepts defined herein. Hence, specific dimensions, directions, or other physical characteristics relating to the embodiments disclosed are not to be considered as limiting, unless expressly stated otherwise. Also, although they may not be, like elements in various embodiments described herein may be commonly referred to with like reference numerals within this section of the application.

Where used herein, the terms “first,” “second,” and so on, do not necessarily denote any ordinal, sequential, or priority relation, but are simply used to more clearly distinguish one element or set of elements from another, unless specified otherwise.

Where used herein, the terms “viewer,” “operator,” “observer,” and “user” are considered equivalents and refer to the person or machine who wears and/or views images using a device having an image light guide. Where used herein, the term “set” refers to a non-empty set, as the concept of a collection of elements or members of a set is widely understood in elementary mathematics. The term “subset,” unless otherwise explicitly stated, is used herein to refer to a non-empty proper subset, that is, to a subset of the larger set, having one or more members. For a set S, a subset may comprise the complete set S. A “proper subset” of set S, however, is strictly contained in set S and excludes at least one member of set S.

Where used herein, the terms “coupled,” “coupler,” or “coupling” in the context of optics refer to a connection by which light travels from one optical medium or device to another optical medium or device.

Where used herein, the term “beam expansion” is intended to mean replication of a beam via multiple encounters with an optical element to provide exit pupil expansion in one or more dimensions. Similarly, where used herein, the terms “expanded image-bearing light beams” and “expanded set of angularly related beams” refer to a light beam replicated via multiple encounters with an optical element to provide exit pupil expansion in one or more dimensions.

Where used herein, the term “about” when applied to a value is intended to mean within the tolerance range of the equipment used to produce the value, or, in some examples, is intended to mean plus or minus 10%, or plus or minus 5%, or plus or minus 1%, unless otherwise expressly specified.

Where used herein, the term “substantially” is intended to mean within the tolerance range of the equipment used to produce the value, or, in some examples, is intended to mean plus or minus 10%, or plus or minus 5%, or plus or minus 1%, unless otherwise expressly specified.

Where used herein, the term “exemplary” is intended to mean “an example of,” “serving as an example,” or “illustrative,” and does not denote any preference or requirement with respect to a disclosed aspect or embodiment.

An optical system, such as a HMD, can produce a virtual image display. In contrast to methods for forming a real image, a virtual image is not formed on a display surface. That is, if a display surface were positioned at the perceived location of a virtual image, no image would be formed on that surface. Virtual image display has a number of inherent advantages for augmented reality presentation. For example, the apparent size of a virtual image is not limited by the size or location of a display surface. Additionally, the source object for a virtual image may be small; for example, a magnifying glass provides a virtual image of an object. In comparison with systems that project a real image, a more realistic viewing experience can be provided by forming a virtual image that appears to be some distance away. Providing a virtual image also obviates the need to compensate for screen artifacts, as may be necessary when projecting a real image.

An image light guide may utilize image-bearing light from a light source such as a projector to display a virtual image. For example, collimated, relatively angularly encoded, light beams from a projector are coupled into a planar waveguide by an input coupling such as an in-coupling diffractive optic, which can be mounted or formed on a surface of the planar waveguide or integrated within the waveguide. Such diffractive optics can be formed as diffraction gratings, holographic optical elements (HOEs), or in other known ways. For example, the diffraction grating can be formed by surface relief. After propagating along the waveguide, the diffracted light can be directed back out of the waveguide by a similar output coupling such as an out-coupling diffractive optic, which can be arranged to provide pupil expansion along one dimension of the virtual image. In addition, a turning grating can be positioned on/in the waveguide to provide pupil expansion in an orthogonal dimension of the virtual image. The image-bearing light output from the waveguide provides an expanded eyebox for the viewer.

As illustrated in, image light guidemay comprise planar waveguidehaving plane-parallel surfaces,. Waveguidecomprises transparent substrate S, which, for example, can be made of optical glass or plastic, having plane parallel first and second surfaces,. In this example, in-coupling diffractive optic IDO and out-coupling diffractive optic ODO are arranged on second surface, and in-coupling diffractive optic IDO is a reflective-type diffraction grating through which image-bearing light WI is coupled into planar waveguide. However, in-coupling diffractive optic IDO could alternately be a volume hologram or other holographic diffraction element, or other type of optical component that provides diffraction for the incoming, image-bearing light WI. In-coupling diffractive optic IDO can be located on first surfaceor second surfaceof planar waveguideand can be of a transmissive or reflective type depending upon the direction from which image-bearing light WI approaches planar waveguide.

When used as a part of a virtual display system, in-coupling diffractive optic IDO couples image-bearing light WI from real image sourceinto substrate S of planar waveguide. Any real image or image dimension is first converted into an array of overlapping angularly related beams encoding the different positions within an image for presentation to in-coupling diffractive optic IDO. Image-bearing light WI is diffracted (generally through a first diffraction order) and thereby redirected by in-coupling diffractive optic IDO into planar waveguideas image-bearing light WG for further propagation along planar waveguideby Total Internal Reflection (“TIR”). Although diffracted into a generally more condensed range of angularly related beams in keeping with the boundaries set by TIR, image-bearing light WG preserves the image information in an encoded form. Out-coupling diffractive optic ODO receives the encoded image-bearing light WG and diffracts (also generally through a first diffraction order) image-bearing light WG out of planar waveguideas image-bearing light WO toward the intended location of a viewer's eye. Generally, out-coupling diffractive optic ODO is designed symmetrically with respect to in-coupling diffractive optic IDO to restore the original angular relationships of image-bearing light WI among outputted angularly related beams of image-bearing light WO. However, to increase one dimension of overlap among the angularly related beams in a so-called eyebox E within which the virtual image can be seen, out-coupling diffractive optic ODO is arranged to encounter image-bearing light WG multiple times and to diffract only a portion of image-bearing light WG on each encounter. The multiple encounters along the length of out-coupling diffractive optic ODO have the effect of enlarging one dimension of each of the angularly related beams of image-bearing light WO thereby expanding one dimension of eyebox E within which the beams overlap. Expanded eyebox E decreases sensitivity to the position of a viewer's eye for viewing the virtual image.

Out-coupling diffractive optics with refractive index variations along a single dimension can expand one dimension of the eyebox by replicating the individual angularly related beams in their direction of propagation along the waveguide between encounters with the out-coupling diffractive optic. In addition, out-coupling diffractive optics with refractive index variations along a second dimension can expand a second dimension of the eyebox and provide two-dimensional expansion of the eyebox. The refractive index variations along a first dimension of the out-coupling diffractive optic can be arranged to diffract a portion of each beam's energy out of the waveguide upon each encounter therewith through a desired first order of diffraction, while another portion of the beam's energy is preserved for further propagation in its original direction through a zero order of diffraction. The refractive index variations along a second dimension of the out-coupling diffractive optic can be arranged to diffract a portion of each beam's energy upon each encounter therewith through a desired first order of diffraction in a direction angled relative to the beam's original direction of propagation, while another portion of the beam's energy is preserved for further propagation in its original direction through a zero order of diffraction.

Out-coupling diffractive optic ODO is shown as a transmissive-type diffraction grating arranged on second surfaceof planar waveguide. However, like in-coupling diffractive optic IDO, out-coupling diffractive optic ODO can be located on first surfaceor second surfaceof planar waveguideand be of a transmissive or reflective type in a combination that depends upon the direction through which image-bearing light WG is intended to exit planar waveguide.

As illustrated in, image light guidemay be arranged for expanding eyebox E in two dimensions, i.e., along both x- and y-axes of the intended image. To achieve a second dimension of beam expansion, in-coupling diffractive optic IDO, having grating vector k, is oriented to diffract a portion of image-bearing light WI toward intermediate optic TO, having grating vector k, which is oriented to diffract a portion of image-bearing light WG in a reflective mode toward out-coupling diffractive optic ODO. Intermediate optic TO may be referred to herein as a turning grating or turning optic. In an embodiment, intermediate optic TO is a surface relief grating. In another embodiment, intermediate optic TO is a holographic optical element. Only a portion of image-bearing light WG is diffracted by each of multiple encounters with intermediate optic TO thereby laterally replicating each of the angularly related beams of image-bearing light WG approaching out-coupling diffractive optic ODO. Intermediate optic TO redirects image-bearing light WG toward out-coupling diffractive optic ODO for longitudinally replicating the angularly related beams of image-bearing light WG in a second dimension before exiting planar waveguideas he image-bearing light WO. Grating vectors, such as the depicted grating vectors k, k, k, extend in a direction that is normal to the diffractive features (e.g., grooves, lines, or rulings) of the diffractive optics and have a magnitude inverse to the period or pitch d (i.e., the on-center distance between grooves) of diffractive optics IDO, TO, ODO. In-coupling diffractive optic IDO, intermediate optic TO, and out-coupling diffractive optic ODO may each have a different period or pitch d.

With continued reference to, in-coupling diffractive optic IDO receives incoming image-bearing light WI containing a set of angularly related beams corresponding to individual pixels or equivalent locations within an image generated by image source. Image source, operable to generate a full range of angularly encoded beams for producing a virtual image, may be, but is not limited to, a real display together with focusing optics, a beam scanner for more directly setting the angles of the beams, or a combination such as a one-dimensional real display used with a scanner. In some examples, image sourcecomprises one or more light-emitting diodes (LEDs), organic LEDs (OLEDs), or ultra LEDs (uLEDs). In other examples, image sourceis a color field sequential projector system operable to pulse image-bearing light of multiple wavebands, for example light from within red, green, and blue wavelength ranges, onto a digital light modulator/micro-mirror array (a “DLP”) or a liquid crystal on silicon (“LCOS”) display. In further examples, image sourceincludes one or more pico-projectors, where each pico-projector is configured to produce a single primary color band (e.g., red, green, or blue). In another example, image sourceincludes a single pico-projector arranged to produce all three primary color bands (e.g., red, green, and blue). In one example, the three primary color bands are a green band having a wavelength in the range between 495 nm and 570 nm, a red band having a wavelength in the range between 620 nm and 750 nm, and a blue band having a wavelength in the range between 450 nm and 495 nm.

Image light guideoutputs an expanded set of angularly related beams in two dimensions of the image by providing multiple encounters of image-bearing light WG with both intermediate optic TO and out-coupling diffractive optic ODO in different orientations. In the original orientation of planar waveguide, intermediate grating TO provides beam expansion in the y-axis direction, and out-coupling diffractive optic ODO provides a similar beam expansion in the x-axis direction. The reflectivity characteristics and respective periods d of diffractive optics IDO, ODO, TO, together with the orientations of their respective grating vectors, provide for beam expansion in two dimensions while preserving the intended relationships among the angularly related beams of image-bearing light WI that are output from image light guideas image-bearing light WO.

While image-bearing light WI input into image light guideis encoded into a different set of angularly related beams by in-coupling diffractive optic IDO, the information required to reconstruct the image is preserved by accounting for the systematic effects of in-coupling diffractive optic IDO. Intermediate optic TO, located in an intermediate position between in-coupling and out-coupling diffractive optics IDO, ODO, is typically arranged so that it does not induce any significant change on the encoding of image-bearing light WG. Out-coupling diffractive optic ODO is typically arranged in a symmetric fashion with respect to in-coupling diffractive optic IDO, e.g., including diffractive features sharing the same period. Similarly, the period of intermediate optic TO also typically matches the common period of in-coupling and out-coupling diffractive optics IDO, ODO. As illustrated in, grating vector kof intermediate optic TO may be oriented at forty-five degrees (45°) with respect to the other grating vectors k, k(all as undirected line segments). However, in an embodiment, grating vector kof the intermediate optic TO is oriented at sixty degrees (60°) to grating vectors k, kof in-coupling and out-coupling diffractive optics IDO, ODO in such a way that image-bearing light WG is turned one hundred and twenty degrees (120°). By orienting grating vector kof intermediate optic TO at sixty degrees (60°) with respect to grating vectors k, kof in-coupling and out-coupling diffractive optics IDO, ODO, grating vectors k, kare also oriented at sixty degrees (60°) with respect to each other (again considered as undirected line segments). The three grating vectors k, k, k(as directed line segments) form an equilateral triangle, and sum to a zero-vector magnitude, which avoids asymmetric effects that could introduce unwanted aberrations including chromatic dispersion.

Image-bearing light WI that is diffracted into planar waveguideis effectively encoded by in-coupling diffractive optic IDO, whether in-coupling diffractive optic IDO uses gratings, holograms, prisms, mirrors, or some other mechanism. Any reflection, refraction, and/or diffraction of light that takes place at in-coupling diffractive optic IDO must be correspondingly decoded by out-coupling diffractive optic ODO to re-form the virtual image that is presented to the viewer. Intermediate optic TO, placed at an intermediate position between in-coupling and out-coupling diffractive optics IDO, ODO, is typically designed and oriented so that it does not induce any change on the encoded light. Out-coupling diffractive optic ODO decodes image-bearing light WG into its original or desired form of angularly related beams that have been expanded to fill eyebox E.

Whether any symmetries are maintained or not among intermediate optic TO and in-coupling and out-coupling diffractive optics IDO, ODO, or whether any change to the encoding of the angularly related beams of image-bearing light WI takes place along planar waveguide, intermediate optic TO and in-coupling and out-coupling diffractive optics IDO, ODO are related so that image-bearing light WO that is output from planar waveguidepreserves or otherwise maintains the original or desired form of image-bearing light WI for producing the intended virtual image.

The letter “R” represents the orientation of the virtual image that is visible to the viewer whose eye is in eyebox E. As shown, the orientation of the letter “R” in the represented virtual image matches the orientation of the letter “R” as encoded by image-bearing light WI. A change in the rotation about the z-axis or angular orientation of incoming image-bearing light WI with respect to the x-y plane causes a corresponding symmetric change in rotation or angular orientation of outgoing light from out-coupling diffractive optic ODO. From the aspect of image orientation, intermediate optic TO simply acts as a type of optical relay, providing expansion of the angularly encoded beams of image-bearing light WG along one axis (e.g., along the y-axis) of the image. Out-coupling diffractive optic ODO further expands the angularly encoded beams of image-bearing light WG along another axis (e.g., along the x-axis) of the image while maintaining the original orientation of the virtual image encoded by image-bearing light WI. As illustrated in, intermediate optic TO may be a slanted or square grating arranged on the front or back (i.e., first or second) surfaces of planar waveguide. Alternately, intermediate optic TO may be a blazed grating.

As illustrated in, in an example embodiment, image light guideincludes in-coupling diffractive optic IDO and out-coupling diffractive optic ODO formed on, in, or along first surfaceof image light guide. In an example embodiment, image light guidefurther includes intermediate diffractive optic TDOand/or intermediate diffractive optic TDO. Alternately, one or more of in-coupling, intermediate, and out-coupling diffractive optics IDO, TDO, TDO, ODO can be formed on, in, or along the second surface of image light guidelocated opposite first surface.

In an example embodiment, image light guidecomprises a split in-coupling diffractive optic IDO including first input region or portionand second input region or portion. First portionis optimized to in-couple light of a first wavelength range (e.g., blue light in the 440-470 nm range or between 450-495 nm) and second portionis optimized to in-couple light of a second wavelength range (e.g., red light in the 630-660 nm range or between 620-750 nm), different than the first wavelength range. First portioncomprises a pattern of diffractive featureshaving first grating vector kand second portioncomprises a pattern of diffractive featureshaving second grating vector k. In an example embodiment, the diffractive features,comprise a plurality of posts. In another example embodiment, the diffractive features,comprise a plurality of linear diffractive features.

It should be appreciated that whileshows the geometric size and shape of first portionand second portionbeing equal, in an exemplary embodiment, first portionmay comprise a geometric size and/or shape that differs from that of second portion.

Out-coupling diffractive optic ODO comprises a first set of diffractive featuresand a second set of diffractive features. First set of grating featuresis optimized to out-couple a first wavelength range of light (e.g., blue light) and second set of grating featuresis optimized to out-couple a second wavelength range of light (e.g., red light). In an exemplary embodiment, as illustrated in, the first and second sets of grating featuresandat least partially overlap and are curved (i.e., curvilinear) or approximate a curve with linear segments to introduce optical power. In an exemplary embodiment, first set of grating featuresis chirped in a first direction, meaning grating featuresprogressively increase in pitch in one direction. For example, as shown in, first set of grating featureshave a pitch dprogressively increasing in pitch in a first direction (i.e., a direction opposite to the direction of grating vector k). In an exemplary embodiment, second set of grating featuresis chirped in a second direction different from the first direction. For example, as shown in, second set of grating featurescomprises pitch dprogressively increasing in pitch in a second direction (i.e., a direction opposite to the direction of grating vector k). In an exemplary embodiment, the pitch progression of second set of grating featuresis equal to the pitch progression of first set of grating features. In other exemplary embodiments, the pitch progression of the second set of grating featuresis not equal to the pitch progression of the first set of grating features.

In an exemplary embodiment, diffractive featuresand/or diffractive featurescomprise square gratings.shows an exemplary embodiment of out-coupling diffractive optic ODO comprising diffractive features having square gratings. Square gratingscomprise pitch d and depth. In an exemplary embodiment, depth/is equal to pitch d/2. In an exemplary embodiment, diffractive featuresand/or diffractive featuresdirectional gratings such as blazed gratings, slanted gratings, or a hybrid thereof. Such grating geometries have a direction sensitivity, i.e., a higher coupling efficiency in a particular propagation direction.shows an exemplary embodiment of out-coupling diffractive optic ODO comprising diffractive features having blazed gratings. In an exemplary embodiment, each of blazed gratingscomprise at least one surface arranged non-parallel to a surface of image light guide.shows an exemplary embodiment of out-coupling diffractive optic ODO comprising diffractive features having slanted gratings. Slanted gratingscomprise pitch d and depth. In an exemplary embodiment, each of slanted gratingscomprise two surfaces that are parallel to each other but non-parallel to a surface of image light guide, and one surface that connects the two surfaces and is parallel to a surface of image light guide.shows an exemplary embodiment of out-coupling diffractive optic ODO comprising diffractive features having hybrid slanted gratings. Hybrid slanted gratingscomprise pitch d and depth. In an exemplary embodiment, each of slanted gratingscomprises two surfaces that are parallel to each other but non-parallel to a surface of image light guide, and one surface that is perpendicular to and connects the two surfaces.

Referring now to, the principal rays that are outcoupled from out-coupling diffractive optic ODO form virtual image V within eyebox E of the user. The diverging principal rays converge at a virtual location in front of image light guidesuch that virtual image V appears at a location at a finite near-focus distance Q in front of image light guide. Thus, each of the angularly related beams of the image-bearing light is no longer collimated, i.e., diverging from a point at infinity, but is instead a beam that appears to diverge from a point located much closer to image light guide. In at least, the diverging principal rays formed by the light rays exiting from image light guideare schematically indicated in solid lines. The dashed lines are extensions of the principal rays that schematically indicate, to the eye of the viewer, the apparent source of the object point in virtual image V.

Virtual image content that appears to be at a shorter focus distance than the conventional infinity focus provides additional control over the way in which virtual images can be presented to viewers such as by presenting images of objects at a perceived distance in front of other objects within the viewer's field of view. Near or finite focal distance Q can be at any distance within about 1 meter to 2 meters, such as at about 0.6 m from image light guide, for example. In order to form a virtual image that appears to have a finite focal distance, each of the angularly related beams of the image bearing light that is emitted from the out-coupling diffractive optic ODO has its principal rays diverging from the apparent location within the virtual image that is positioned at the near focus distance Q. The near focusing of each of the otherwise collimated beams among the set of angularly related beams does not change the relative positions at which the beams appear to be focused within the virtual image. Instead, the entire virtual image appears closer to the viewer.

One mechanism for converting a dimension of a collimated beam propagating along the image light guideinto a diverging beam representing a near focus position in a virtual image is presented inas a stepped-chirp diffraction grating(e.g., comprising diffractive featuresof out-coupling diffractive optic ODO) operating in a reflective mode. Grating vector kextends parallel to the x-axis in a direction opposite to the direction along which the collimated beam is propagated. Grating period d of diffraction gratingincreases in a stepwise manner along the same direction of propagation. Because the angle through which a given beam is diffracted is inversely proportional to the period of a diffraction grating, the angle through which the collimated beam is diffracted decreases with successive encounters of the collimated beam along the stepped-chirp diffraction grating. At the start of diffraction grating, first encountered by the collimated beam, period d is relatively shortened so that the diffraction angle is increased and at the end of grating, period d is relatively lengthened so that the diffraction angle is decreased.

Considered in the x-z plane, stepwise adjustments to period d along the x-axis length of diffraction gratingprovide for diffracting the representative collimated beam through progressively varying diffraction angles so that the light appears to emanate from near-focus point f. The other angularly related beams of image bearing light WG are also diffracted through a progression of different diffraction angles with each successive encounter with diffraction gratingso that the light from each of these beams appears to emanate from a different near-focus point elsewhere in a common focal plane at distance Q in accordance with their differing angular content.

As described above, it should be appreciated that it is not necessary to optimize for out-coupling of green light as the wavelength range for green light falls between the wavelength ranges of red and blue light. Thus, in an exemplary embodiment, image light guideoptimizes for red light and blue light, and green light will be in-coupled by diffractive features,of in-coupling diffractive optic IDO, albeit potentially less efficiently. It should be further appreciated that image light guideis operable to optimize two spectral ranges or wavelengths (i.e., for any pitch/wavelength range), and is not limited to optimization of just red and blue light.

In an exemplary embodiment, image light guidefurther comprises turning gratings or intermediate diffractive optics TDO, TDO. In an exemplary embodiment, the path for each wavelength range of image-bearing light includes in-coupling optic IDO, intermediate diffractive optic TDOand/or intermediate diffractive optic TDO, and out-coupling diffractive optic ODO. In image light guide, image-bearing light WG is directed from in-coupling diffractive optic IDO to intermediate diffractive optics TDO, TDOafter even numbers of incidents upon diffractive features, and image-bearing light WG is directed from intermediate diffractive optics TDO, TDOto out-coupling diffractive optic ODO after odd numbers of incidents upon diffractive features. It should be appreciated that image light guidedescribed herein could be utilized to introduce 2D eyebox expansion.

With reference to, in an example embodiment, in-coupling diffractive optic IDO is configured to direct a portion of a first wavelength range of image-bearing light WGtoward intermediate diffractive optic TDO, having third grating vector k, which is oriented to diffract a portion of image-bearing light WGin a reflective mode toward out-coupling diffractive optic ODO. In an exemplary embodiment, only a portion of image-bearing light WGis diffracted by each of multiple encounters with intermediate diffractive optic TDO, thereby laterally replicating each of the angularly related beams of image-bearing light WGdirected to out-coupling diffractive optic ODO. In an embodiment, intermediate diffractive optic TDOincludes a pattern of linear diffractive features.